The present invention refers to unsaturated polyester resins which are not inhibited by the oxygen of the air, and which do not exhibit persistent residual surface tackiness, containing a particular type of additive which will be specified hereinafter. Further, the present invention refers to a process for the preparation of said unsaturated polyester resins. Other objects will be specified hereinafter.
It is known that in the hardening of unsaturated polyester resins, atmospheric oxygen has an inhibiting effect on the cross-linking which occurs through a radicalic mechanism. Said phenomenon is more or less marked depending on the type of resin. For many unsaturated polyester resins, it causes a residual tackiness to remain on the surface exposed to the air, which tackiness persists even after many months. The tackiness is all the more accentuated the smaller the thickness of the resin body. This is harmful particularly in the use of unsaturated polyester resins (glass fibre reinforced polyesters), as the tackiness of the products causes difficulty in stacking the products, adhesion of powder on the surface, of the products, and other drawbacks.
In order to avoid said drawbacks it is known to employ solid paraffins at room temperature as additives to unsaturated polyesters. The paraffins, however, decrease the adhesion between the resin layers to an extent that they will separate, particularly under fatigue stresses.